Electron beam scan converter

ABSTRACT

A scan converter has a storage type target electrode in which information may be stored by means of a writing beam for subsequent retrieval by means of a reading beam. The electron output of a channel multiplier plate, positioned on the writing gun side of the target electrode, is proximity focused upon that target. The operating potentials of the writing system are selected to establish high electron velocity of the writing beam through the field of the writing beam deflectors to minimize transit time distortion and are further arranged to introduce a decelerating field at the input of the channel plate to attenuate the electron velocity to a value for optimum gain in that plate.

United States Patent [191 Wolski Oct. 16, 1973 [73] Assignee: Ni Tec, Inc., Niles, Ill.

[22] Filed: Feb. 12, 1971 [21] Appl. No.: 115,073

Related US. Application Data [63] Continuation of Ser. No. 838,573, July 2, 1969,

abandoned.

[52] US. Cl. 315/12, 315/11 [51] Int. Cl. H0lj 29/41 [58] Field of Search ..315/1l, 12,15

[56] References Cited UNITED STATES PATENTS 2,922,906 1/1960 Day, Jr. et a1. 313/103 X 3,039,017 6/1962 Brown et a1. 315/11 3,174,070 3/1965 Moulton 315/18 X 3,182,221 5/1965 Poor, Jr. 315/12 X 3,408,530 10/1968 Gibson, Jr 315/12 3,673,457 6/1972 Sackinger et al.. 315/12 2,922,906 1/1960 Day, Jr. et a]. 313/103 X 3,039,017 6/1962 Brown et a1. 315/11 3,174,070 3/1965 Moulton 315/18 X 3,182,221 5/1965 Poor, Jr. 315/12 X Primary Examiner-Carl D. Quarforth Assistant Examiner-P. A. Nelson Attorney-Francis W. Crotty [57] ABSTRACT A scan converter has a storage type target electrode in which information may be stored by means of a writing beam for subsequent retrieval by means of a reading beam. The electron output of a channel'multiplier plate, positioned on the writing gun side of the target electrode, is proximity focused upon that target. The operating potentials of the writing system are selected to establish high electron velocity of the writing beam through the field of the writing beam deflectors to minimize transit time distortion and are further. arranged to introduce a decelerating field at the input of the channel plate to attenuate the electron velocity to a value for optimum gain in that plate.

14 Claims, 5 Drawing Figures PAIENIEDum 16 I975 SHEET 1 BF 2 umg Inventor AdolphJ.Wolski z gamwfif A mm 5 Om Ho ey' nnm 16 ms 3.766426 sum 2 or 2 Adolphdwolski ELECTRON BEAM SCAN CONVERTER This is a continuation of application Ser. No. 838,573, filed July 2, 1969, now abandoned.

BACKGROUND OF THE INVENTION The present invention is addressed generally to an electron beam scan converter and has a wide range of applications. It is suited, for example, to converter devices which feature an electrical input signal as well as an electrical output signal; these devices are generally typified by a storage target electrode which-stores the input signal for subsequent retrieval as an output signal. Another attractive application of the invention is one wherein an electrical input signal is converted to a visual output. In order to avoid unnecessarily burdening the disclosure, it will be confined to a consideration of these two forms of converter.

Converters, as such, are quite well known particularly as to the two forms presently under consideration. They find application in handling transient information of exceedingly short duration whether the information be repetitive or nonrepetitive. By way of illustration, the scan converter of the prior art is perfectly capable of accommodating pulse information having a duration of 20 nanoseconds. Obviously, to accommodate signals of such exceedingly short duration, the time base for controlling the writing beam must be extraordinarily fast. As a consequence, the electron density of the writing beam over the target electrode is insufficient to support signal to noise ratios that are desired. This suggests the introduction of electron gain made possible, for example, by the interposition of an electron multiplier in the path of the writing beam. The practical difficulty that presents itself in attempting to adapt the channel plate type of electron multiplier to the writing portion of a scan converter is the apparent incompatibility of the requirements of electron beam velocity imposed to minimize transit time distortion on the one hand and to achieve optimum gain with the channel multiplier on the other. The present invention constitutes an attractive and practical solution to this problem, making it possibe to improve scan converters as to signal to noise while preserving their high frequency response.

Accordingly, it is an object of the invention to provide a new and improved electron beam scan converter.

It is a more specific object of the invention to provide such a converter featuring enhanced gain and, therefore improved signal to noise ratio.

Still another object is to introduce scan magnification into a converter.

It is a subsidiary object of the invention to provide an improved form of channel multiplier for augmenting the gain of such a converter.

SUMMARY OF THE INVENTION An electron beam scan converter, embodying the invention, comprises a channel multiplier plate disposed transversely of a reference path and having a gainelectron velocity characteristic which peaks in a predetermined range of values of input electron velocity and decreases with velocity values above that range. There ing and accelerating along the path of the converter toward the multiplier plate an electron beam with an electron velocity in'the field of the deflectors that ex- BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularlity in appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 is a schematic representation of a scan converter featuring an electrical input and an electrical output;

FIG. 2 is a curve representing the gain-electron velocity characteristic of a typical channel multiplier plate;

FIG. 3 is a detail representing a form of travelling wave deflector that may be used in the device of FIG. 1;

FIG. 4 shows a modification of the target element that may be used in the scan converter or in a camera tube and featuring a unique arrangement for accomplishing electron multiplication as well as signal storage;

and FIG. 5 represents a converter having an electrical input but providing a visual output.

Aside from the inclusion of a channel multiplier plate and an unusual arrangement of operating potentials, the scan converter of FIG. 1 is of conventional construction featuring a storage target with-a reading beam disposed to one side thereof and a writing beam disposed to the other side. More specifically, the target electrode has a conductive backing plate 10 disposed transversely of a reference path A, here shown as the longitudinal axis of an evacuated envelope 11. The backing plate has a coating 12 of several microns thickness of a material which exhibits the property of electron bombardment induced conductivity. Semiconductive materials are suitable for this purpose and such materials as zinc sulphide, barium fluoride, lead oxide, magnesium fluoride, arsenic trisulphide and antimony trisulphide have been used successfully in preparing storage electrodes similar to target structure 10, 12. This target is not only capable of storing data in the form of a charge pattern but it also introduces gain through induced conductivity and is generally referred to in the art as an EBIC target. Obviously, backing plate 10 must be thin enough to be electronpermeable and a suitable material for it is aluminum.

Further gain is introduced into the converter by means of an electron multiplier, specifically, a channel multiplier plate 15 disposed transversely 'of reference path A and having a gain-electron velocity characteristic which peaks in a certain range of input electron velocities to be considered more particularly hereafter. This component is also a known structure and is disclosed, by way of illustration, in U.S. Pat. No. 3,341,730, issued in the name of George W. Goodrich et al. on Sept. 12, 1967. As indicated in the drawing,

it is an array or stack of parallel arranged individual channel or tubular elements usually formed of glass and treated to the end that the inner surface of each channel is a secondary emitter with an emission ratio, in response to an input or impacting electron, greater than unity. The channels, after having been arrayed to define a plate of suitable dimension anc donfiguration, are subjected to a heat treatment to fuse the channel elements and form a single unitary multichannel plate. The diameter of the individual channels is usually small compared with their length. It is necessary to apply an operating potential across the plate and for that purpose both the input and output surfaces are provided with a conductive coating or layer as by painting, vapor deposition, or the like to which terminals 16, 17 are attached for convenience of applying an operating potential to the plate. Channel plate is so arranged in relation to target 10, 12, both as to position and potential level, to achieve proximity focusing of electrons issuing from plate 15 upon the storage target. It will be observed that the storage target is maintained at d.c. ground potential and the potential applied to the channel plate is selected, not only in relation to the target in order to achieve proximity focusing but also, in a manner to be described hereafter, in relation to the writing electron gun of the converter to achieve an optimum gain contribution from the channel plate and further to achieve scan magnification.

To the side of EBIC target 10, 12 opposite plate 15 is the usual reading electron gun comprising a cathode and first and second control grids 21 and 22 which are followed by an anode and unipotential focus lens arrangement 23. When energized, this electrode system develops an electron beam and accelerates it in the direction of target 10, 12. The beam is caused to scan that target by two pairs of electrostatic deflection plates, shown as a pair 24 of vertical deflectors and a pair 25 of horizontal deflectors. Immediately adjacent EBIC layer 12 of the target is the usual ring type collector electrode 26 to which an output terminal 27 is coupled through a capacitor 28. The potential applied to collector 26 is chosen to establish an electric field of sufficient intensity to achieve EBIC gain in the target and a representative value of +10 volts is shown in the drawing. The geometry of the electrode arrangement, including its spacing from and the thickness of insulation of layer 12, causes the field across the target in terms of volts per centimeter to be very high, sufficient for EBIC action.

The writing electron gun system is similar comprising a cathode 30, first and second grids 31 and 32, and an anode and focusing electrode arrangement 33. Likewise, there are similar pairs of deflection electrodes, comprising vertical deflectors 34 and horizontal deflectors 35. These deflectors are maintained at d.c. ground potential, as indicated, and terminal 350 of the horizontal pair connects with a source (not shown) of time base deflection signal while the corresponding terminal 340 of the vertical deflectors connects to a source (not shown) of information signal that is to be translated.

It has been convenient in the drawing to show a typical pair of electrostatic plates for vertical deflectors 34 but it may be highly desirable in certain installations to use as the ungrounded plate of the vertical deflectors an arrangement of the type shown in FIG. 3. This is a travelling-wave type of deflector with a zig-zag pattern 34 of a conductor disposed on an insulating substrate and arranged to face the grounded deflector plate. As is well understood from travelling-wave theory, the dimensions of conductive element 34' are chosen so that the velocity of travel, measured in the direction of reference axis A, of a signal transversing conductor 34' is the same as the speed of an electron of the writing beam passing through the field of deflectors 34. Where these velocites are properly correlated, an added deflection sensitivity is achieved.

Whatever specific structural form is adopted for the deflectors, and certainly they may be electromagnetic as well as electrostatic, consideration is to be given to the possibility of transit time distortion. This distortion is minimized by reducing as far as practicable the transit time of the electrons of the writing beam in traversing the field of the deflector. There are at least two degrees of freedom; (a) in selecting the physical length of the deflector measured along reference path A, and (b) in adjusting the velocity of the electrons as determined, for example, by the operating potential of cathode 30. If the deflector is made short and the beam velocity is high to minimize transit time distortion the deflection sensitivity is impaired. In general, a compromise is chosen to achieve optimum bandwidth or high frequency response by minimizing transit time distortion while at the same time establishing useful deflection sensitivity. A representative value of the axial length of the deflectors, for a frequency of 200 MHz, is 2 inches and a representative value of cathode potential is -10 kv. The other voltages of FIG. 1 are representative values that are found to provide efficient operation of the scan converter.

The electron beam velocity of the writing beam, as thus far described, is that attributable to the I 0 kv potential of cathode 30 which, while a satisfactory value from the standpoint of transit time distortion, is very much higher than the electron velocity desired for optimum gain of channel plate 15. The gain of that plate varies with velocity in the manner shown in FIG. 2 and if the desired range of input velocity for optimum gain is designated by values v and v it will be found that the maximum value of the range is far less than that resulting from an accelerating potential of 10 kv and more typically is that corresponding to an accelerating potential of the order of 5002,000 volts. Consequently, means are provided for establishing between the deflectors and the input of channel plate 15 a decelerating field for decreasing the electron velocity of the beam at the input of the channel plate to a value within the range required for optimum gain. This is accomplished by the potential established at the input of the channel plate in relation to cathode 30 of the writing gun. For the illustrative values indicated in the drawing, the potential gradient between the cathode and the input of the plate is of the order of I kv and a similar voltage is applied across the channel plate.

Of course, envelope 11 is evacuated and the various components of the tube are mechanically supported within it. Moreover, the reading and writing beams function sequentially or simultaneously, giving rise in some installations to the need of gating or switching but, in this respect, the arrangement of FIG. 1 is similar to prior art devices and consequently these matters are not dealt with in the drawing or description; they are well known.

In operating the described scan converter, the reading beam is energized and time base signals for scanning are applied to terminals 24a and 25a of the reading beam deflection plates. At this time, the writing system is de-energized. Initially, the free surface of EBIC layer 12 is scanned by the reading beam and the secondary electrons emitted from that surface in response to scanning by the reading beam are collected by collector 6. In this fashion, the surface of the target is brought to a uniform potential level or charge condition. The target is now prepared to receive a data or information signal that is to be stored, and the reading beam may be turned off.

With the target thus established at a reference potential, the writing beam is energized and is deflected in the line scan direction in response to the time base signal applied to terminal 35a to establish a time varying field between deflectors 35. During its line traverse, the beam receives a vertical deflection in response to the information signal applied to terminal 34a and, preferably, the time-base signal is synchronized or timed in relation to the transient signal to be stored to the end that the transient occurs well within the writing beam trace time. Additionally, the potential of cathode 30 is selected at a value such that the electrons of the beam travel at a high velocity in traversing the fields of deflection plates 34, 35 in order to attain minimal transit time distortion. As electrons of the beam pass beyond the deflectors they encounter a decelerating field since the potential difference between cathode 30 and the input to plate 15 is materially less than that between cathode 30 and the deflectors. Hence, the beam electrons are decelerated as they approach channel plate 15 to enter the channels thereof with a reduced velocity appropriate for optimum channel gain. In passing through the channels of plate 15, the input electrons are multiplied in the usual way and the ooutput electrons of the channel plate are focused upon the target to penetrate backing layer and impinge upon EBIC layer 12. This electron bombardment induces conductivity within the target electrode and provides additional gain on an incremental area basis in layer 12 as the beam crosses over the target in response to the horizontal and vertical deflection effects. The conduction discharges selected elemental areas of the target, determined by the path of travel of the writing beam under the influence of deflectors 34 and 35, and establishes a charge distribution or pattern that represents the stored information signal. After the target has been scanned by the writing beam, storing the information signal therein, the writing beam is deenergized and the stored information may be read out at a subsequent time by the reading beam.

The subsequent scanning of the target by the reading beam, in restoring target 10, 12 to a uniform potential level, gives rise to signal currents flowing in the circuit of collector 26. For example, when the reading beam strikes an elemental area of the target that has been discharged by the writing beam, an enhanced collector current flows as that area is restored to the reference charge condition. On the other hand, when the reading beam is incident upon an elemental target area that remains at the reference charge level, there is no such enhanced collector current. In this fashion, currents representing the stored information are developed as the reading beam scans the target. Those currents are applied through capacitor 28 to any utilizing device desired (not shown).

tential a signal amplifier coupled to collector 26 is not disturbed by spurious signalssuch as d.c.ripple which would interfere with the signal processing. Not only does the scan converter have the gain available with the EBIC target, it further hasthe gain of the channel multiplier 15, and the resulting electron density on the target improves the signal'to noise ratio. Even though the electron beam velocity is sufficiently high in the region of deflectors 34, 35 to minimize transit time distortion,

the electrons impact channel plate 15 with a proper,

attenuated velocity to derive maximum gain from the .plate. Output signals of the order of nanoamperes for a writing rate of 500 inches per microsecond have been attained at a readout rate of 1.75 seconds per frame.

The modification of FIG. 4, which shows channel plate 15 to an enlarged scale, is unique in that the multiplier also serves the function of image storage. For that purpose, the output surface of the plate, .that is the surface closer to collector 26, is covered with a layer 15 of a material having the property of secondary emission. An insulating material, such as zinc sulphide,

is evaporated to a thickness of a few'microns over the conductive layer that otherwise terminates the endsurface of the plate. The insulating layer covers all portions of the surface of the platethat immediately surround the output terminations of its various channels. With this modification, target 10, 12 may be omitted, also eliminating the proximity focusing that isvnecessary in the structure of FIG. 1. In using the modified arrangement in the converter of FIG. 1, the end of plate 15 adjacent collector electrode 26 is established at ground potential and scanning of that end of the plate by the reading beam establishes surface layer 15 at a uniform reference charge or potential by its secondary emission effect in response to scanning and to the field resulting from the collector electrode potential. The insulating surface will have been brought to a uniform positive potential so that electrons which traverse the channels of plate 15 during the writing function, are captured by the insulating layer 15 to thus store the information signal. It may subsequently be derived by scanning with the reading beam. Of course, the arrangement may, if desired, have the input to target 15 generated by a known form of photoemissive cathode, instead of the described writing gun, as in a pick-up or camera tube. In such .a case, and as shown schematically in broken-line construction in FIG. 4, the input 50 of the image converter is a photoemissive cathode structure which responds to a radiant-energy image 51 that is focused in the cathode by a lens 52 to develop a corresponding electron image. Usually, such a cathode structure is a sandwich or multi-layer arrangement having, for example, a foundation or substrate which is transparent to the form of energy for which a response is desired and having, thereover'fluorescent or similar layer for converting the radiant image to a light image. A photosensitive layer is superposed over the fluorescent layer and sometimes there ia an interposed barrier layer to prevent unwanted chemical interactions. Cathode structures of this type are well known in the art and when energized develop an electron image which is accelerated and focussed upon the input or entrance of channel by an electro-optical system indicated by cylindrical electrode 53. This image experiences mutliplication within channel plate 15 and is stored in storage layer 15' at the exit or output termination of the channel plate for subsequent use. In one well understood pick-up or camera system, a reading beam scans layer 15' and derives an electrical signal representative of the stored image.

The converter of FIG. 5 is similar to that of FIG. 1 except that in this instance the information is displayed visibly rather than being stored for susequent derivation. Accordingly, the tube has a fluorescent screen 40 at the end opposite writing cathode and the screen may have the usual backing layer 41 of aluminum. In this modification, as thus far described, the information signal, amplified by the gain of channel plate 15, is focused on screen where the electrons issued from plate 15 excite the screen, converting the information signal into a visible image. A further modification of FIG. 5 is the introduction of electrodes 42 and 43 between the deflectors and channel plate 15. Electrode 42 has an applied operating potential of the value required to establish the desired decelerating field as explained in conjunction with the operation of FIG. 1. Electrode 43 is used to terminate the anode and deflection fields and to establish along with electrode 42 a uniform decelerating field. And, in this case, the input of plate 15 is maintained at the same potential as electrode 42 so that there is a field free space between electrode 42 on the one hand and the input of channel plate 15 on the other hand. This has the advantage of greater flexibility in the decelerating field and presents the additional possibility of scan magnification.

If the field of electrode 42 is along reference axis A, it reduces the velocity component of electrons along the same axis but has no effect on the velocity component in a vertical plane which represents the information signal. Since the axial component has been re duced, the net of these velocity components is a vector that is further angularly displaced from the tube axis than would be the case without the influence of the decelerating field and, therefore, a consequent scan magnification.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An electron beam tube comprising:

a channel multiplier plate disposed transversely of a reference path and having a gain-electron velocity characteristic which peaks in a predetermined range of values of input electron velocity and decreases with velocity values exceeding said range;

first means disposed about said path and responsive to an applied time-base signal for deflecting an electron beam in one direction across said plate;

second means disposed about said path and responsive to an applied information signal for deflecting said electron beam in another direction across said plate, at least one of said deflection means introducing a transit-time distortion that decreases with increase in the electron velocity of the electron beam;

electron gun means for developing, and accelerating along said path toward said plate, an electron beam having an electron velocity in the field of said one deflection means that exceeds said predetermined range;

and means for establishing between said one deflection means and said plate a decelerating field for decreasing the electron velocity of said beam at the input of said plate to a value within said range.

2. An electron beam tube in accordance with claim 1 wherein said tube is a scan converter in which a target electrode is disposed transversely of said reference path in a position to be impacted by electrons emerging from said multiplier plate.

3. A scan converter in accordance with claim 2 in which said target electrode is a semi-conductor electrode having the property of electron bombardment induced conductivity.

4. A scan converter in accordance with claim 2 in which said target electrode is maintained substantially at d.c. ground potential.

5. A scan converter in accordance with claim 4 in which at least one of said deflection means is of the electrostatic type and likewise is maintained at d.c. ground potential.

6. An electron beam tube in accordance with claim 1 in which said means for establishing said decelerating field comprises means for applying a potential to the input of said plate.

7. An electron beam tube in accordance with claim 6 in which said electron gun means includes a cathode maintained at a potential level which, in relation to the potential level of said one said deflection means, establishes as electron velocity in the field of said one deflection means that exceeds said predetermined range and which, in relation to the potential level of said plate, establishes said decelerating field.

8. An electron beam tube in accordance with claim 1 in which said means for establishing said decelerating field comprises an electrode disposed transversely of said reference path between said one deflection means and said plate and means for maintaining said electrode at an operating potential of such value as to establish said decelerating field.

9. An electron beam tube in accordance with claim 8 where said electrode is disposed between said deflecting means and said plate.

10. An electron beam tube in accordance with claim 8 in which the input of said plate is maintained at the same operating potential as said electrode to establish a field-free space therebetween.

11. An electron beam tube in accordance with claim 1 in which said channel multiplier plate is provided with means, located at the output end of said plate, for responding to the output electrons issuing from said plate to store information represented by said output electrons.

12. An electron beam tube in accordance with claim 11 in which the output surface of said plate is covered with a layer of material having the property of secondary emission.

13. An electron beam display tube comprising:

a channel multiplier plate disposed transversely of a reference path and having a gain-electron velocity characteristic which peaks in a predetermined range of values of input electron velocity and decreases with velocity values exceeding said range;

first means disposed about said path and responsive to an applied time-base signal for deflecting an electron beam in one direction across said plate;

second means disposed about said path and responsive to an applied information signal for deflecting said electron beam in another direction across said plate, at least one of said deflection means introducing a transit-time distortion that decreases with increase in the electron velocity of the electron beam;

electron gun means for developing, and accelerating along said path toward said plate, an electron beam 10 having an electron velocity in the field of said one deflection means that exceeds said predetermined range;

means for establishing between said one deflection means and said plate a decelerating field for de-' creasing the electron velocity of said beam at the input of said plate to a value within said range comprising an electrode disposed transversely of said reference path between said one deflection means and said plate and means for maintaining said electrode at an operating potential of such value as to establish said decelerating field; and means including a phosphor screen adjacent to said plate opposite said decelerating means for providing a visible image corresponding to said applied information signal. 14. An electron beam display tube in accordance with claim 13 in which said means for establishing said decelerating field comprises means for applying a potential to the input of said plate. 

1. An electron beam tube comprising: a channel multiplier plate disposed transversely of a reference path and having a gain-electron velocity characteristic which peaks in a predetermined range of values of input electron velocity and decreases with velocity values exceeding said range; first means disposed about said path and responsive to an applied time-base signal for deflecting an electron beam in one direction across said plate; second means disposed about said path and responsive to an applied information signal for deflecting said electron beam in another direction across said plate, at least one of said deflection means introducing a transit-time distortion that decreases with increase in the electron velocity of the electron beam; electron gun means for developing, and accelerating along said path toward said plate, an electron beam having an electron velocity in the field of said one deflection means that exceeds said predetermined range; and means for establishing between said one deflection means and said plate a decelerating field for decreasing the electron velocity of said beam at the input of said plate to a value within said range.
 2. An electron beam tube in accordance with claim 1 where said tube is a scan converter in which a target electrode is disposed transversely of said reference path in a position to be impacted by electrons emerging from said multiplier plate.
 3. A scan converter in accordance with claim 2 in which said target electrode is a semi-conductor electrode having the property of electron bombardment induced conductivity.
 4. A scan converter in accordance with claim 2 in which said target electrode is maintained substantially at d.c. ground potential.
 5. A scan converter in accordance with claim 4 in which at least one of said deflection means is of the electrostatic type and likewise is maintained at d.c. ground potential.
 6. An electron beam tube in accordance with claim 1 in which said means for establishing said decelerating field comprises means for applying a potential to the input of said plate.
 7. An electron beam tube in accordance with claim 6 in which said electron gun means includes a cathode maintained at a potential level which, in relation to the potential level of said one said deflection means, establishes an electron velocity in the field of said one deflection means that exceEds said predetermined range and which, in relation to the potential level of said plate, establishes said decelerating field.
 8. An electron beam tube in accordance with claim 1 in which said means for establishing said decelerating field comprises an electrode disposed transversely of said reference path between said one deflection means and said plate and means for maintaining said electrode at an operating potential of such value as to establish said decelerating field.
 9. An electron beam tube in accordance with claim 8 where said electrode is disposed between said deflecting means and said plate.
 10. An electron beam tube in accordance with claim 8 in which the input of said plate is maintained at the same operating potential as said electrode to establish a field-free space therebetween.
 11. An electron beam tube in accordance with claim 1 in which said channel multiplier plate is provided with means, located at the output end of said plate, for responding to the output electrons issuing from said plate to store information represented by said output electrons.
 12. An electron beam tube in accordance with claim 11 in which the output surface of said plate is covered with a layer of material having the property of secondary emission.
 13. An electron beam display tube comprising: a channel multiplier plate disposed transversely of a reference path and having a gain-electron velocity characteristic which peaks in a predetermined range of values of input electron velocity and decreases with velocity values exceeding said range; first means disposed about said path and responsive to an applied time-base signal for deflecting an electron beam in one direction across said plate; second means disposed about said path and responsive to an applied information signal for deflecting said electron beam in another direction across said plate, at least one of said deflection means introducing a transit-time distortion that decreases with increase in the electron velocity of the electron beam; electron gun means for developing, and accelerating along said path toward said plate, an electron beam having an electron velocity in the field of said one deflection means that exceeds said predetermined range; means for establishing between said one deflection means and said plate a decelerating field for decreasing the electron velocity of said beam at the input of said plate to a value within said range comprising an electrode disposed transversely of said reference path between said one deflection means and said plate and means for maintaining said electrode at an operating potential of such value as to establish said decelerating field; and means including a phosphor screen adjacent to said plate opposite said decelerating means for providing a visible image corresponding to said applied information signal.
 14. An electron beam display tube in accordance with claim 13 in which said means for establishing said decelerating field comprises means for applying a potential to the input of said plate. 